Armature coil



C. F. JENKINS ARMATURE COIL July 15, i935,

Filed Nov. ll', 1955 INVENTOR 7795 FJQn/ms.

ATTORNEY Patented July 16, 1935 ARMATURE COIL Charles F. Jenkins, Wilkinsburg', Pa., assigner to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application November 11, 1933, Serial No. 697,638

20 Claims. (Cl. 171-206) My invention relates to armature coils and it has particular relation to such coils for directcurrent railway motors, although it is not limited to any particular application.

In direct-current railway-motor design, it is being found that the limit in the output or rating of the motors is determined in many cases by the commutation or life of the commutator and brushes. It is well known that when commutation is poor, the commutator surface becomes roughened, and when commutation is good, the surface of the commutator takes on a polish under the action of the brushes. If the balance between the polishing action of the brushes and the roughening action of sparking due to poor commutating conditions is overstepped, the commutator ceases to operate with a bright polished surface, resulting in unsatisfactory operating conditions involving frequent maintenance operations and a short life of commutator and brushes.

In direct-current railway motors having a plurality of coils per slot, particularly with reference to motors utilizing one-turn armature-coils having integral or one-piece coils made from copper strap without resorting to the welding together of two or more strap conductors at the ends, in order to make one complete coil, it has invariably been the practice to dispose the coil-sides in the natural order in which they would come, with the result that one of the end coils, of the group of coils which lie half in the bottom of one slot and half in the top of another slot, will have its bottom coil-side disposed in the very bottom of the slot in which it lies. This has resulted in poor I commutating conditions when the direction of rotation is such that this coil is the last one oi the group to leave the commutator brush. This is because, when the group of coils in any pair of slots are being commutated, all of the shortcircuited coils, on leaving the brush and thus becoming open-circuited, can transfer their energy by induction to another short-circuited coil or coils in the same slots, the coupling being close because of the juxtaposition of. the coils in the same slots. The last coil has no closely coupled short-circuited coil to which it can transfer its energy, with the result that this energy must be dissipated in a spark at the coinniutator, and if this last coil has one of its coil-sides at the bottom of a slot, it will be in a position to have the maximum reactance of all of the coil-sides in that slot, thus producing the maximum sparking.

An object of my invention is, therefore, to produce a commutator-type dynamo-electric machine having such disposition of the coil-sides, in

a machine of the type just described, that the last coil to be commutated, in a group of a plurality of coils lying in a given pair of slots, shall not have one of its coil-sides in the bottom of the slot, for either direction of rotation.

A further object of my invention is to accomplish the foregoing result in a stepped-slot armature, such as that which is illustrated in my Patent No. 1,916,374, patented July fi, 1933.

The stepped-slot design of. my patent just mentioned is somewhat restricted in its scope to a design in which the bottom portions of the slots are approximately half as wide as the top p01'- tions thereof.

A further object of my present invention is to provide a stepped-slot armature of the integral stepped-coil type in which the strap conductor is twisted or rotated through 90 in passing from the top of one slot to the bottom of another, so that there is no iixed relation beween the widths of the top and bottom portions of the stepped slot, thus making it possible for the designer to change these dimensions, to suit the conditions of design, by the simple expedient of changing the shape of the cross-section of the copper strap.

With the foregoing and other objects in view, my invention consists in the apparatus, structure and combinations hereinafter described and claimed and illustrated in the accompanying drawing, wherein:

Figure l is a diagrammatic development view showing the arrangement of the end-connections and commutator-bars of a dynamo-electric machine embodying my invention;

Fig. 2 is a diagrammatic transverse sectional view through an armature shown in Fig. l, with the rear end-connections shown diagrammatically;

Fig. 3 is a perspective view of the rear end-connections of Figs. l and 2;

Fig. 4 is a cross-sectional view showing the disposition of the armature conductors in a slot in a slightly different embodiment of my invention; and

Figs. 5 and 6 are similar views showing still further modifications.

As shown in Figs. 1, 2 and 3, my invention is applied to a commutator-type dynamo-electric machine, which may be a reversible direct-current motor, comprising a slotted laminated armature core l2 having an armature winding I3 thereon, only a few coils of the armature winding being shown, for convenience in illustration. The front ends I4 of the armature-winding conductors are connected to the commutator-bars yl5 of a commutator i6, which is engaged by brushes l? and 03 for carrying the current to or from the commutator. The armature winding i3 has rear end-connections iQ-Which are special, in accordance with my invention.

The particular armature winding shown is made from strap-conductors. The winding, as shown in Figs. i, 2 and 3, is composed of a plurality of single-turn coils per slot. In Figs. l, 2 and 3, there are four coils per slot. It will be noted that the entire winding is made up of straight coil-sides, which lie in the slots., andY iront and rear end-connections ifi and it. VI-lalf of the coil-sides lie in the top portions of the slots and are designated as top coil-sides 2 i, and half oi the coil-sides lie in the bottom portions and are designated as bottom coil-sides 22. These two groups of coil-sides Vare usually wrapped together with special ground insulation, as `indicated in Fig. 1 at 23, which also considerably facilitates the handling of the coils in assembling the armature.

The armature core is preferably provided with slots that are stepped, as indicated at 2d in Fig. 2, the top half of the slot being wider and shallower than the bottomhalf, so as to provide a greater section between the roots of the teeth between the slots, as pointed out in my aforementioned patent. Y

In common with vthe construction shown in my above-mentioned patent, the embodiment of my invention in Figs. i, 2 and 3 utilizes a construction kin which there are twice as many top coilsides 2i in side-by-side relation, that is, in a row, counting rfrom side to side, in the top portion oi each slot as there are bottom coil-sides 22 in sideby-side relation in the bottom portion o1 each slot, and twice as many bottom coil-sides in4 superposed relation, that is, in a iile, counting from top to bottom, in the bottom portion of each slot as there are top coil-sides 2l in superposed relation in the top portion of each slot.

In the embodiment of my invention shown in Figs. l, 2 and 3, there are four top coil-sides 2l, numbered i, 2, 3 and i to distinguish them, all

' disposed in a row, counting from side to side, in

the top portion of each slot. The front end-connections lli of these four coil-sides go to four successiye commutator-bars l5, which are numbered i, 2, 3 and i in order to distinguish them from each other.

The rear end-connections i3 and i9 are arev rangedwith a loop 712@ which is devised, as shown more clearly in Fig. 3; namely, so that the iirst Y and last strap-conductors, numbered l andfi, re

spectively, if considered as coming from the top coil-sides, come out side-by-side on top; the otherv two strap-conductors 2 and 3, if also considered as coming fromthe top coil-sides, come out below l and il; and all four conductors continue on into4 the-bottom coil-sides 22 disposed in another slot, as indicated in Figs. 1 and 2, so that the disposi-- tion of the coil-sides in the bottom halves of the slot are two abreast and two deep.

It will be observed, with the foregoing arrangement in Figs. 1,2 and 3, that as the brushes l'l and i8 leave the last coil of Athe group of four coils in each pair of slots, thus open-circuiting the coil, it will open-circuit either coil number y l or coil number li, according to the direction off rotation, and the design is such that the bottom coil-sidesof both of these coils are disposed as far from the bottom of the slot Efi as possible, soas to reduce the reactance of these coils which commutate last and thus haverthe most sparking. v

My invention is particularly applicable to an integral coil construction in which the armature winding isrmade up of a plurality of one-piece units or coils, each made from a single integral piece of strap-conductor, and each comprising a top coil-side in one slot and a bottom coil-side in another slot, and the end-connections therefor, as illustrated in Figs. l and 3. In order that the coils may all be exactly alike, such a construction usually utilizes a plan in which the four bottom coil-sides, numbered l to li, are al1 together in a single slot instead of having the bottom coilside l or fi in the bottom of another slot, as is sometimes practiced in split-throw windings or" the type covered by a Hellmund Patent No. 1,238,795, patented April l, 1919. My invention is obviously not limited, in its broadest aspects, in either one or" these two particulars, that is, integral construction, orV constant-pitch coils.

It will be observed that if the two bottoni coilsides, numbered i and 1,V or l and n, if there are n coils per slot instead or" four, are to be disposed; away from the bottom of the slot, as just decribed, there must be more than two coils per slot, so that there will be atleast one other bottem coil-side which can be disposed underneath the bottom coil-sides numbered i and n, respec-v tively. Fig. 4 illustrates the wayrthe invention would be arranged where n is equal to three, the coilsides being numbered consecutively l, 2 and 3 in the manner explained Vin connection with Figs. l to 3.

It will be noted that the embodiment of my present invention, as shown in Figs. l, 2 and 3, is limited tof a stepped-slot shapein which they bottom half of the slot is approximately onehali as wide and twice as deep as the top halt, the slight departure from anexa-ct approznrna tion of these dimensions being due to the presence of the ground insulation and whatever slot liner is utilized. In order to avoid this desigm limitation, I have devised the winding arrangements shown in Figs. 5 and 6.

One essential feature of the invention shown in Figs. 5 and e is that the rear end-connections of the conductors are so arranged that the ccnductors are rotated or twisted through 90, so that oi each slot and edgewise in the bottom or" each slot,v as shown in Fig. 5, or vice versa, as shownin Fig. 6. Another essential et this winding that there are twice as many conductors in de `r in superposed relation, in the top haii of e ch slot as there are conductors in width, or by--side relation, in the bottom half, and twice as many vconductors in depth in the bottoni haii as there are conductors in width in the top halt, This arrangement, asA shown in Figs. 5 Aand '3, has the advantage over that shown in Figs. to 3 in that there is no lined rela :on between the widths of the top and bottom halves 'of the slot, so that these dimensions can be changed to suit the conditions or" design by changing the length and breadth of the rectangular cross-section oi thD strap conductors'. In general, a iiat strapconductor wil1 be utilized, in the designs of the type shown in Figs. 5 and 6, rather than a square` sectioned strapconductor.

In the above description of the embodiments of riy invention shown in Figs. 5 and 6, the word',

twice could be replaced by thrice or, in gen-v eral, by m times, where mis any integer greater than l, which would result in af possible arrange# ment where very deep slots are required...

In Fig. 5, there are six one-turn lcoils per slot, the successive coils being numbered from l to t. ln other Words, n is bere equal to sin, and it will be observed that tne bottom coil-sides of the first and last coil in each group, numbered i and 5, rcspcctiv ly, are both in tbe top rank of tbctivo changes rorn tne essential tea my inve E desire, therefore, that tbe appended clain s. vall be accorded the broadconotruction consistent with their language and tbe prior I claini as iny invention:

i. A con Yiutator-type dynamo-electric Inacliine having a slotted armature-core and an armature-winding liaving n coils per slot, n being greater than two, bali of the coil-sides, bereinafter called top coil-sides, being disposed in tbe top lia es o the slots, and ti e other bali oi the coilu es, hereinafter called bottom coilsides, being disposed in the bottoni halves of the slots, a group of n top coil-sides in any slot being connected to n consecutive connnutator-bars and being electrically continuous, respectively, with a corresponding group of bottom coil-sides all lying in the bottom half or" another given slot, characterized by tbe two bottornA coilsides ich correspond to the first and nth coil-- sides of said group ci n top-coil sides being disposed the top portion of the bottoni nali or" oornrnutator-type dy'nanio-electri rnacbine having a stepped-slot armature core and an ainiaturewinding having n coils per slot, n ter tiran tro, half oi the coil sides, called top coil-sides, beine dispose arrow r than the top lialves or" the o n. to n consecutive commutatorbais and being electrically continuous, respec t" fely, vfit'n a corresponding group of bottoni coilall lying in tbe bottom bali of another given slot, characterized by tbe two bottom coil-sides which 'espond to the rst and nth coil-sides of said group of n topuooil sides being disposed in tbe top portion of the bottom half oi said seeond vientioned slot, with another bottom coilside o sides disposed underneath said two bottom coil-sides.

3, A coinnfiutator-type dynamo-electric niacbine having a slotted armature-core and a strap-conductor armature-winding liaving n coils per slot, n being greater than two, halt of the coil-sides, hereinafter called top coil-sides, being disposed in the top halves of the slots, and tbe other half or" tbe coil-sides, hereinafter' called bottoni coil-sides, be g disposed in tne bottoni naive-s oi tbe slots, s .d armature-winding coinprmng plurality oi one-piece units each made from a single integral piece of strap-conductor and each comprising a top-coil side in one slot and a bottom coil-side in another slot and tbe end-connections therefor, tbe bottom coil-sides in any slot being disposed in a plurality of superposed ranks, a group of n top coil-sides in any given slot being connected to 7L consecutive coinrnutator-bers, the bottom coilesides corresponding to both the rst and btb of these n top coil-si es being disposed in a rank or ranks other than tbe bottoni` rank,

4. A commutator-type dynamo-electric machine having a stepped-slot armature core and tbe coil-sides, hereinafter called top coilsides,

D the ot botto being disposed in tbe bottoni bali/es i f tbe bottom halves of the slots being deeper and narrower than tbe top nalves of slots, sV id armature-winding comprising a plurality oi one-piece units each made iroin a single integra" 1 of strap-conductor and each comprising side in one slot and a bottom` coil-side in another slot and tbe endconnectio -s t eroici', the bottom coilesides in any slot being di osed in a plurality oi superA osed A of n top coil-sides in any given slot being connected to n consecutive corornutator-bars, the bottoni coil-sides corresponding to bot'n tbe rst and nth of these n top coil-sides being disposed in a rank or ranks other than the bottoni rank.

5. coinrnutator-type dynamo-electric inacliine having an armatore comprising a core bavstepped slots the top portion of the slots being approximately twice as Wide and half as deep as the bottom portion, and armature-winding having n coils per slot, 1t being greater than tivo, bali of the coil-sides, hereinafter called top coil-sides, being disposed in tbe top portions of tbe slots, and tbe other bali oit tbe coil-sides, hereinafter called bottomcoil-sides, being disposed in tbe botto-rn portions of tbe slots, characterized by even number of coil-sides lying in each portion of eeen slot, there being twice as many coil-sides in a row, counting from side to side, n tbe top por ion of each slot as in tbe bottom portion of eac'n slot, and twice as many coil-sides in a le, counting from top to bottoni, in tne bottom portion of each slot asin the top portion oi eacb slot, tbe bottoni coil-sides. in any slot bein disposed in a plurality oi superposed re" is, group of n top oeil-sides in any given slot bu i g con ected to n consecutive commutatorbars, tne bottom coil-sides corresponding to botbl the first and nth of these 11. top coil-sides being dispo -d in a rank or ranks other than tbe botn torn rank.

A cr -tvpe dynamo-electric niacbine nav sQeppd-olot armature core and coil-sides in a le, counting from top to F bottoni, the bottom portions oi eac'n slot as in tbc top porti n of each slot, tbe bottoni coil-sides in any slet b disposed in a plurality of superranks, the n top coil-sides in any given slot beinT connected to n consecutive commutatorbars, the bottom coil-sides corresponding to both the iirst and 11th of these 1L top coil-sides being disposed in a rank or ranks other than the bottom rank.

'7. A commutator-type dynamo-electric machine having a stepped-slot armature core and an armature-winding having 1t one-turn coils'per slot, 11 being an even number' greater than two, each coil comprising a single top coil-side lying in the top portion. of one slot and a single bottom coil-side lying in the bottom portion of another slot, each slot having 1t top coil-sides disposed in side-by-side relation and 11. bottom coil-sides disposed in 11i/2 superposed ranks of two each, the 11 top coilnsides in any given slot being connected to 11, consecutive ccmmutator-bars, the bottom Y coil-sides corresponding to both the iirst and nth of these 11y top coil-sides being disposed in a rank or ranks other than the bottom rank.

8. A cornmutator-type dynamo-electric machine having a stepped-slot armature core and an armature-winding having four onewurn coils per slot, each coil comprising a single top coilside lying in thetop portion of one slot and a single bottom coil-side -ying in the bottom portion or" another slot, each slot having four top coil-sides disposed in side-by-side relation and four bottom coil-sides disposed in two superposed ranks of two each, the our top coil sides, in any given slot being connected to four consecutive commutator-bars, the bottom coil-sides corresponding to both the `first and fourth of these four top coilsides being disposed in the top rank or" the bottom coil-sides.

9. A oommutator-type dynamo-lectric machine having a stepped-slot armature core and an armature-winding having 1i coils per slot, 1t being greater than two, half of the coil-sides, hereinafter called top coilsides, being disposed in the top halves of the slots, and the other half of the coil-sides, hereinafter called botto-m coilsides, being disposed in the bottom halves of the slots, the top and bottom coil-sides being of at strap-conductors lying iiatwise in one hah ci each slot and edgewise in the other half, there being twice as many conductors in a iile, counting from top to bottom, in they top half or" each slot as there are conductors in a row, counting from side to side, in the bottom half, and twice as many conductors in a iile, counting from top to bottom, in the bottom half as there are conductors in a row, counting iro-1n side tol side, in the top half, a group of 1t top coil-sides in any given slot being connected to 1L consecutive commutator-bars and being electrically continuous, respectively, with a corresponding number of bottom coil-sides all lying in the bottom half of another given slot, characterized by the two bottom coil-sides which correspond to the rst and nth coil-sides of said group of 11 top coil-sides being disposed in the top portion of the bottom half of said secondmentioned slot, with another bottom coil-side or sides disposed underneath said two bottom coilsides.

10. A commutator-type dynamo-electric machine having a stepped-slot armature core and an armature-winding having 11 coils per slot, 1t being greater than two, half of the coil-sides, hereinafter called top coil-sides, being disposed in the top halves of the slots, and the other half of the coil-sides, hereinafter called bottom coil-sides, being disposed in the bottom halves of the slots, said armature-winding comprising a plurality or one-piece units each made from a single integral piece of flat strap-conductor and each comprising a top-coil side in one slot and a bottom coil-side in another slot and the endconnections therefor, there being a twist in the end-connections whereby the strap-conductors lie flatwise in one half of the respective Slots and edgewise in the other half, there being twice as many conductors in a le, counting from top to bottom, in the top half of each slot as there are conductors in a row, counting from side to side, in the bottom half, and twice as many conductors in a iile, counting from top to bottom, in the bottom half as there are conductors in arow, counting from side toside, in the top half, a group of 11, top coil-sides in any given slot being connected to 11 consecutive commutator-bars and being continuous, respectively, with a corresponding number of bottom coil-sides all lying in the bottom half oi another given slot, characterized by thetwo bottom coil-sides which correspond to the nrstand 11th coi1-sides` of said group of 11-top coil sides being disposed in the top portion of the bottom half` o1 said second-mentioned slot, with another bottom coil-side or sides disposed underneath said two bottom coil-sides.

li. A commutatortype dynamo-electric maie having'a stepped-slot armature core and an armature winding having 11 one-turn coils per slot, 11 being an even number greater than two, each coil comprising a single top coil-side lying in the top portion of one slot and a single bottom coil-side lying in the bottom portion of another slot, the top and bottom coil-sides being of strep-conductors lying iiatwise in one half or each slot and edgewise in the other half, there being twice as many conductors in a file, counting from top to bottom, in the top half of each slot as there are conductors in a row, counting Yfrom side to side, in theY bottom half, and twice as many conductors in a iile, counting from top to bottoni, in the bottom half as there are conductors in a row, Counting from side to side, in the top half, a group of 1L top ooil-sides in any given slot being connected to 11 consecutive commutator-bars and being electrically continuous, respectively, with a corresponding number of bottom coil-sides all lying in the bottom half of another given slot, characterized'by the two bottom coil-sides which correspond to the rstrand nth coil-sides of said group of 11, top coil-sides being disposed in the top portion of the bottom half of said second-mentioned slot, with another bottom coil-side or sides disposed underneath said two bottom coil-sides. n

l2. A commutator-type dynamo-electric inachine having a stepped-slot armature core and an armature-winding having 1L coils per slot, 1L being greater than two, half of the coil-sides, hereinafter called top coil-sides?, being disposed in the top halves of the slots, and the other half or" the coil-sides, hereinafter called bottom coilsides, being disposed in the bottom halves of the slots, the top and bottom coil-sides being of flat strap-conductors lying atwise in one-half or each slot and edgewise in the other half, there being m times as many conductors in a file, counting from top to bottom, in the top half of each slot as there are conductors in a row, counting from side to side, in the bottom half, and m times as many conductors in a iile, counting from top to bottoni, in the bottom half as there are conduetors in a row, counting from side to side, in the top hair, m being greater than unity, the bottom coil-sides in any slot being disposed in a plurality of superposed ranks, a group oi 11 top coil-sides in any given slot being connected to n consecutive coinniutat-or-bas and being eiectrically continuous, respectively, with a co responding num--n ber of bottom coil-sides, characterized by the two bottoni coil-sides which correspond to the rst and nth coih: of said group of n top coiisides being disposed. in rank or ranks other than the bottoni rank.

elynanio-electric rnachi ot Y ltine anti ons per slot, n b the coil-sides, h

ein a single trapcontinctor and each coil-siete inone slot and a botiot the eci-cone' Sii" twist in the p--ooncletors :tive siete nel being times a row, eounte half, m being om coil-sides in any of super-posed given slot consecn ive commntator noone, respectively, with a er of bottom coil-sides, charo bottom eoihei .es which core t and. nth coil-sides of said. b disposed. in a rank e bottom rank. 'oi-type dynamo-electric ma- 'epnerllot armature core and aving n one-turn coils than two, each coil comeoii-siiie 'lying in the top poro` a single bottornL oeil-.si

portion of another slot, e top nsides b o1" hat strap-conclueM one haii of each slot and other i, there being m times y conduotors in a le, counting from top toni, in the ton half of each slot as there are conductors row, counting from side to side, in the bottom heli, and m times as many conductors in a nie, counting from top to bottom, in the bottom half there are conductors in a row, from side to side, the top half, m Y tenter than unity, the bottom coil-sides in any slot be i posed a group of n top coil-sides in any given slot being connected to n consecutive comiars and electrically continuous,

' a corresponding number of bot- ,with tono ooi -sides, ch racterized by the two bottom coil-sides which corespone, to the rst and nth coil-ei es of group oi n top coil-sides being disposed in a rank or ranks other than the bottom rank.

1.5. A dynamo-electric machine having a stenped-slot armature core and an armaturewin 'ig having n coils per slot, n being greater than two, halt of the coil-sides, hereinafter called top coil-sides, being disposed in the top halves of the slots, and the other half oi the coil-sides, hereinafter caiied bottom coil-sides, being disposed in the bottom halves oi the slots, the top and bottom coil-sides being of flat strap-conductors lying fiatwise in one half of each slot and edgewse i the other haii, there being twice as many conductors in a iile, counting from top to bottom, in the top haii of each slot as there are condnctors fig from side to side, twice as conductors Mn top to bottom, in the bote e conductors in a row, counteine in the top half. o o-electric machine having a core and an armatureg n oeils per slot, n being greater the coil-sides, hereinafter called Le eingdisposeel in the top halves and the other haii of the coil-sides, called bottom coil-sides, being discom icing a plurality of one-piece units each made Ytroni a single integra-1 piece of iiat stran-coi^=nctor and each comprising a top coihside in one siot and a bottom coil-side in another siot and. the end-connections therefor, there being a 9G twist in the enel-connections whereby .p-oonfluctors lie iatwise in one half of the f f "l Tewise in the other half, n any conductors in a le, torn, in the top half of conductors, c row, countie, :in the bottoni halt, anr eters in a file, counting from bottom halt as there are a row, counting from side to p half.

dynamo-electric machine having :i an armaturecoils per siot, n being i i two, each ooii comcoi stie ying in the top It and single bottom coil-side portion ot another slot, the `i ysing of strapof each slot twice '-ting from top e en eiot as there a row, counti" g from side to e bottom half, and ce es many conin a iiie, counting from top to bottom,

. be ving n s n. e

side,

rowJ in the ton half.

i8. A dynamo-electric machine having a p-. -sl.ot arr@ 1e core and an armatures 'oer siot, n being greater o es, hereinafter called sposecl in the top halves the other half of the coil-sides, hereinafter called bottom coil-sides, being disposed in bottom halves of the slots, the top and bottom coii-sioies being of iiat straponmotors lying flatwise in one half of each slot and edgei e in the other hah, there being m rl i,

s a row, counting from side to i the bottom half, and m times as many conductors in a ie, counting troni top to bottoni, 1n the bottom as there are conductors in a counting from side to side, in the top hait, being greater than unity.

i9. A dynamo-electric machine having a stepped-slot armature core and an armature- Y `Winding having n coils per slot, n being greater than two,-ha1f of the coil-sides, hereinafter called Y top Coil-sides, being disposed in the top halves of the slots, and the other half of the coil-sides, hereinafter called bottom coil-sides, being disposed in the bottom halves of the slots, said armature-winding comprising a plurality of onepiece units each made from a single integral pieee'of flat strap-Conductor and each comprising a top coil-side in one slot and a bottom coilsideV in another slot and the end-connections therefor, there being a 90 twist in the end-connections Wherebythe strap-conductors lie flatwise in one'hali of the respective slots and edgewise inthe other half, there being m times as many conductors in a. le, counting from top to bottom, in the top half of each slot as there are conductors 'm a row, counting from side to side, in the bottom half, and m times as many conductors in a file, counting from top to bottom, in the bottom half as there are conductors in a row, counting from side to side, in the'top half; m being greater than unity.

20. A dynamo-electric machine having a stepped-slot armature core and an armature- Winding having 'n one-turn coils per slot, n being greater than two, each coil comprising a single top coil-side lying in the top portionY of one slot and a single bottom coilside lying in the bot'- tom portion of another slot, the top and bottom ,coil-sides being of at strap-conductors lying latwise in one half of each slot and. edgewise in Ythe other half, there being m times as many confrom side to side, in the top half, m being greater Y than unity. Y

CHARLES F. JENKINS. 

